The present invention concerns a multi-step transmission.
Such a transmission has been disclosed by EP 0 434 525 A1, which encompasses, essentially, an input drive shaft and an output drive shaft, which are arranged coaxial to one another, a double planetary gear set placed concentric to the output drive shaft and five shifting elements in the form of three shift elements and two brakes, the selective blocking of which respectively determine, pairwise, the different gear ratios between the input drive shaft and the output drive shaft.
The known transmission possesses two power paths, wherein a first element of the double planetary gear set is connected by means of a first shift element with the first power path. A second element of the double planetary gear set is connected to the output drive shaft and a third element is connected with the second power path by means of a third shift element and is braked by means of a first brake. A fourth element of the double planetary gear set is connected with the first power path by means of a second shift element and is braked by a second brake, so that a selective shifting pairwise between the shifting organs assures that six forward gear positions are available. This arrangement then comprises a first gear through the first shift element and the first brake, a second gear through the first shift element and the second brake, a third gear through the first shift element and the second shift element, a fourth gear through the first shift element and the third shift element, a fifth gear through the second shift element and the third shift element a sixth gear through the third shift element and the second brake, and finally, a reverse gear position through the second shift element and the first brake.
The purpose of the present invention is to be found in the creating of a multi-step transmission, which encompasses at least seven forward gear positions with a favorable gear step and ample spread, and is relatively economical to manufacture.
An essential advantage is to be found in the fact, that the invented multi-step transmission offers at least seven forward gear positions with a reduced number of gear sets and shift elements. In each gear, into which a shift is made, only two shift elements are actuated. By the shifting from one gear to the next, simply one shift element was open and another shift element was closed. In this way, a GroupWise shifting of critical shifting quality, in which a plurality of shift elements must be shifted simultaneously, is avoided.